We used historical data to trace trapped protons observed by the Fengyun-1C (FY-1C) satellite at low Earth orbits (~800 km) and chose data at 5–10 MeV, 10–40 MeV, 40–100 MeV, and ~100–300 MeV from 25 March to 18 April 2000 to analyze the proton variations. Only one isolated strong storm was associated with a solar proton event during this period, and there was no influence from previous proton variations. Complex dynamic phenomena of proton trapping and loss were affected by this disturbance differently depending on the energy and L location. The flux of 5–10 MeV protons increased and created new trapping with a maximum at L ~2.0, and the peak flux was significantly higher than that at the center of the South Atlantic Anomaly. However, at higher L, the flux showed obvious loss, with retreat of the outer boundary from L ~2.7 to L ~2.5. The increase in the 10–40 MeV proton flux was similar to that of the 5–10 MeV flux; however, the peak flux intensity was lower than that at the center of the South Atlantic Anomaly. The loss of the 10–40 MeV proton flux was closer to the Earth side, and the outer boundary was reduced from L ~2.3 to L ~2.25. For the higher energy protons of 40–100 MeV and 100–300 MeV, no new trapping was found. Loss of the 40–100 MeV protons was observed, and the outer boundary shifted from L ~2.0 to L ~1.9. Loss was not obvious for the 100–400 MeV protons, which were distributed within L < 1.8. New proton trapping was more likely to be created at lower energy in the region of solar proton injection by the strong magnetic storm, whereas loss occurred in a wide energy range and reduced the outer boundary on the Earth side. Similar dynamic changes were observed by the NOAA-15 satellite in the same period, but the FY-1C satellite observed more complex changes in lower energy protons. These results revealed that the dynamic behavior of protons with different L-shells was due to differences in the pitch angle. Possible mechanisms related to new trapping and loss are also discussed. These mechanisms are very important for understanding the behavior of the proton belt in the coming solar cycle.
Geomagnetic storms and substorms play a central role in both the daily life of mankind and in academic space physics. The profiles of storms, especially their initial phase morphology and the intensity of their substorms under different interplanetary conditions, have usually been ignored in previous studies. In this study, 97 intense geomagnetic storms (Dstmin ≤ –100 nT) between 1998 and 2018 were studied statistically using the double superposed epoch analysis (DSEA) and normalized superposed epoch analysis (NSEA) methods. These storms are categorized into two types according to different interplanetary magnetic field (IMF) Bz orientations: geomagnetic storms whose IMF is northward, both upstream and downstream relative to the interplanetary shock, and geomagnetic storms whose upstream and downstream IMF is consistently southward. We further divide these two types into two subsets, by different geomagnetic storm profiles: Type I/Type II — one/two-step geomagnetic storms with northward IMF both upstream and downstream of the interplanetary shock; Type III/TypeIV — one/two-step geomagnetic storms with southward IMF both upstream and downstream of the interplanetary shock. The results show that: (1) geomagnetic storms with northward IMF both upstream and downstream of the interplanetary shock have a clear initial phase; geomagnetic storms with southward IMF in both upstream and downstream of the interplanetary shock do not; (2) the IMF is an important controlling factor in affecting the intensity characteristics of substorms. When Bz is positive before and after the interplanetary shock arrival, the Auroral Electrojet (AE) index changes gently during the initial phase of geomagnetic storms, the median value of AE index is maintained at 500–1000 nT; (3) when Bz is negative before and after the interplanetary shock arrival, the AE index rises rapidly and reaches its maxmum value about one hour after storm sudden commencements (SSC), although the time is scaled between reference points and the maximum value of AE is usually greater than 1,000 nT, representing intense substorms; (4) for most cases, the Dst0 usually reaches its minimum at least one hour after Bz. These results are useful in improving contemporary space weather models, especially for those that address geomagnetic storms and substorms.